1. Field of the Invention
This invention relates generally to well logging tools, and more particularly to a continuous obstruction monitor installed between the drill string and the logging tool which utilizes drilling fluid to indicate when the logging tool has encountered an obstruction and allows for transporting and setting of the logging tool, circulation through the monitor housing, and reciprocation of the drill pipe while continuously monitoring for borehole obstructions.
2. Brief Description of the Prior Art
Systems which transport well logging tools on the drill string are known in the art. Conventional systems incorporate a cable and wet connect transport assembly or locomotive which is forced down the borehole by mud pressure within the drill string to make the electrical connection to the logging tool. A side door sub in the drill string allows the cable to be run along the outside of the pipe for some distance downhole. The side door sub permits the cable to enter the pipe and seals it to prevent loss of drilling mud pressure. In the logging operation, with the tool at the total depth and electrical connection from the logging tool to the surface, drill pipe is removed one joint at a time while the cable is spooled in at the same rate. The present invention is used in conjunction with conventional wet connect cable transport assemblies or locomotives, side door subs, logging tools, and utilizes state of the art logging procedures.
The most common method of transporting the logging tool is to mount the logging tool on the drill string enclosed in a protective sleeve with openings to allow sensors to contact the borehole from within the sleeve. Distorted data curves sometimes occur due to the proximity and interference from the sleeve. The only indication of an obstruction in this type of system is when the drill string stops which often causes damage to the logging tool or the sleeve. Attempts at circulating the obstruction away using the openings in the sleeve is limited because the circulation is above the obstruction.
Another common method of transporting the logging tool is to mount the logging tool on the drill pipe with a shock absorbing device to protect the tool while monitoring obstructions electrically with a tension device downhole. This eliminates sleeve interference, but because of side door sub cable limitations, satisfactory electrical connection is not always possible. A well with a 2,500 foot kick out depth (point at which bore begins to deviate from vertical) and 12,500 feet in total depth would leave 10,000 feet of hole to traverse without a weight indicator. If an obstruction is encountered, circulation can be made at the top of the tool string but not at the obstruction location at the bottom of the string.
Another transport method is one which utilizes protective sleeves mounted on the drill string with the logging tool retained by a complex latch mechanism. This system uses a two piece wet connect cable transport assembly which separates after being latched to the logging tool. Releasing the latch mechanism allows the logging tool to be lowered from the protective sleeve for the logging operation. The complexity of the latching system makes it prone to numerous failures. Because most of the drilling fluid escapes at the latch assembly, only a small amount of circulating fluid is directed to the obstruction. The logging tool may also be blocked in the sleeve by debris from the obstruction building up in the sleeve.
There are several patents which disclose apparatus for monitoring or measuring pressure while drilling and supporting sensing devices in well logging tools.
Conley et al, U.S. Pat. No. 3,965,978 discloses a subsurface transient pressure indicator suitable for for shutting off fluid flow through tubing at a subsurface location in a completed well containing a packer in the tubing-casing string annulus. The device has a seating nipple forming a part of the tubing string positioned at the downhole location at which it is desired to shut off fluid flow through the tubing. The nipple has an upwardly facing shoulder, and a main plug member having a downwardly facing seating area is adapted to seat in the seating nipple. The main plug member is connected to the surface of the well by a wireline or cable. A port extends through the main plug below the point of seal with the nipple to a second seating area and a second port from the second seating area to a point above the point of seal. A pressure measuring means communicates with the tubing space below the point of seal. A relief plug is adapted to seat in the second seating area of the main plug. Pressure is equalized in the tubing string above and below the device by pulling upwardly on the wireline to pull the relief plug body away from the second seating area.
This device measures transient pressure in a completed well and is quite different than the present invention which is a transport system for well logging tools which is transported on drill pipe and functions as a continuous obstruction monitor independent of cable connections.
Claycomb, U.S. Pat. No. 4,184,545 discloses a measuring and transmitting apparatus comprising an elongate tubular member functioning as a drill collar and adapted to to be placed in a drill string while drilling a well. The apparatus utilizes a mud driven motor, while the mud flows therethrough functioning as a drill collar and out the bottom. The motor creates electric power which is used to operate transducers forming measurements which are encoded. The encoding portion of the equipment utilizes an oil reservoir, a mud driven pump, a valve which dumps the oil back to the reservoir if there is no signal and which otherwise delivers it to a spool valve which drives a modulated signal generator. The signal generator modulated the back pressure in the mud flow by restricting the mud flow, thereby forming a signal which is sensed in the mud flow path. This device modulates mud flow through it and must have a surface mud pump attached to function.
Garney, U.S. Pat. No. 4,359,900 discloses an elongated well logging instrument having a lever latch and positioning mechanism attached to a carriage and a snorkel and barrel assembly. One end of a pressure sensing device is mounted on the carriage and the snorkel is affixed to the opposite end. The latch and positioning mechanism allows the assembly to be moved until the snorkel enters the barrel and retains it in place. The mechanism is then secured in place. The mechanism contains an indicator which is visible if the mechanism is not in a position to be secured. Electrical signals are passed from the sensing device, through the snorkel to an electrical connector at the end of the barrel and through a cable to the surface.
Peppers et al, U.S. Pat. No. 4,483,394 discloses a hydraulic power unit for for a downhole instrument of a measurement while drilling system. The hydraulic unit is enclosed within a drill collar that is connected to a drill string of a rotary drilling rig. An outer body sleeve is rigidly mounted in the instrument drill collar, and a fixed inner sleeve is connected to the outer body sleeve in a concentric relation. A longitudinally movable plunger assembly is supported between the outer sleeve and inner sleeve and movable in a telescopic fashion between an extended position and a retracted position to provide hydraulic power fluid for the operation of hydraulically powered circuits of the instrument.
The prior art in general, and these patents in particular, do not disclose the present invention of a continuous obstruction monitor installed between the drill string and the logging tool which utilizes drilling fluid to indicate when the logging tool has encountered an obstruction and allows for transporting and setting of the logging tool, circulation through the monitor housing, and reciprocation of the drill pipe while continuously monitoring for borehole obstructions.